1. Field of the Invention
The present invention relates to a navigation system.
The present invention further relates to a navigation device.
The present invention further relates to a navigation server.
The present invention further relates to a vehicle provided with a navigation device.
The present invention further relates to a group of such vehicles.
The present invention relates to a navigation method.
2. Related Art
Nowadays GPS navigation facilities are available that can relatively accurate determine a position of a vehicle. However, in some circumstances alternative navigation methods are required as satellite signals required for GPS-navigation are not always available, for example at locations below sea level and in buildings. One such alternative method applies dead-reckoning using data obtained from odometers or inertial sensors, for instance gyroscopes and accelerometers. Gyroscopes provide information about the orientation of the vehicle and accelerometers provide information about its acceleration. If the initial position and velocity of a vehicle are known, its momentaneous velocity and position can be estimated by numerical integration of the acceleration and orientation data obtained from the accelerometers and gyroscopes. Generally accelerometers have a systematic error, also denoted as bias, resulting in a drift in position indication, exponential in time. Accordingly, such navigation devices based on inertial sensors need to be calibrated periodically to measure and compensate the sensor biases. With low-cost sensors, and without bias compensation, the navigation solution becomes useless within minutes.
This also applies to dead reckoning methods using other sensors, e.g. odometers for measuring speed and a compass for measuring direction.
Also systems are known that use a combination of GPS-navigation and navigation by dead-reckoning. For example U.S. Pat. No. 6,801,855 provides systems and methods for complementary navigation devices with various integrated positioning functionality. In particular the navigation method includes providing a first navigation device having a triangulation positioning functionality and providing a second navigation device adapted to communicate with the first navigation device. The second navigation device includes one or more dead reckoning positioning components. The one or more dead reckoning positioning components are used in complement to the triangulation positioning functionality to determine the position when the triangulation positioning functionality is degraded. In the known systems and methods the first and the second navigation device are arranged in a single vehicle.
In case navigation on the basis of inertial sensing, inaccuracies result from a bias in the measured acceleration. This bias may have several causes, some of them are:                1. A bias caused by the accelerometers.        2. A bias in the measurement of the orientation. The latter bias is due to imperfections of the gyroscopes, internal alignment errors in the navigation device and orientation initialization errors of the navigation device.        